JP2007208586A - Radio communication system and radio communication equipment - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an excellent radio communication system and radio communication equipment which employ reflected wave transmission method and can perform data transmission suitably by returning a modulated reflected wave on which transmission data is superimposed by a reflector to non-modulated carrier sent from a reflected wave reader side, the radio communication system and radio communication equipment enabling the power consumption thereof to be reduced by suppressing useless transmitting/receiving operations in a terminal side mounted with the reflector and in a host mounted with the reflected wave reader. <P>SOLUTION: When no transmission data exists and no data frame is received from the host, the terminal waits for the generation of data to be transmitted for some time and subsequently starts data transmission, and defines a control frame for notifying transmission and reception stop time information between the terminal and the host to notify each other of the next transmitting/receiving timing. When receiving a control frame, the transmission and reception operations are stopped on the basis of the transmission and reception stop time information and the transmission and reception operations are restarted after the elapse of the stop time. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a wireless communication system and a wireless communication apparatus in which a reflector returns a modulated reflected wave in which transmission data is superimposed on an unmodulated carrier wave transmitted from a reflected wave reader, and in particular, there is transmission data. The present invention relates to a wireless communication system and a wireless communication apparatus that reduce power consumption by suppressing unnecessary transmission / reception operations in a reflector and a reflected wave reader.

  As an example of wireless communication means that can be applied only locally, an RFID system is widely known. RFID was originally developed as a device including identification information and a readable / writable storage area. In addition, since the RFID system can be realized with low power consumption, recently, replacement of wireless data communication with an RFID system from a conventional wireless LAN or Bluetooth communication has been studied.

  Examples of the communication method of the RFID system include an electrostatic coupling method, an electromagnetic induction method, and a radio wave communication method. Among them, the radio wave communication type RFID system includes a reflector that transmits data by a reflected wave obtained by modulating a received unmodulated carrier, and a reflected wave reader that reads data from a modulated reflected wave signal from the reflector. A reflected wave transmission that is configured (see, for example, Patent Document 1) and is also referred to as a “backscatter method” is performed.

  When a non-modulated carrier is sent from the reflected wave reader, the reflector modulates the reflected wave and superimposes data based on an antenna load impedance switching operation or the like. That is, since no carrier generation source is required on the reflector side, the data transmission operation can be driven with low consumption. An antenna switch for changing the load impedance of the antenna is generally composed of a gallium arsenide IC, and its power consumption is several tens of μW or less. Therefore, in reflected wave transmission, data transmission is possible at several tens of μW, which is an overwhelming performance difference compared to the average power consumption of a general wireless LAN (for example, see Patent Document 2). In addition, since a terminal equipped with a reflector only performs an operation of reflecting a received carrier, it is not regarded as a radio station, and is treated as a target not subject to legal regulations imposed on radio wave communication.

  Reflected wave transmission is considered to be particularly effective in a communication mode in which a transmission ratio in one direction from a terminal equipped with a reflector to a host equipped with a reflected wave reader occupies most of the communication. For example, a battery-driven mobile device such as a digital still camera, a digital video camera, or a mobile phone is used as a data transmitter, and a host device such as a personal computer that displays, reproduces, prints out, stores, or manages data is used as a data receiver. Consider a data communication system. In this case, a reflector is mounted on the mobile device side, and a non-modulated carrier is sent from the reflected wave reader connected to the host device, so that still images, videos, and music data are not burdened on the mobile device battery. It is possible to read (upload) a relatively large amount of data.

  In addition, a radio communication system has been proposed that employs a time-division multiplexing method with variable frame length for reflected wave transmission between a host equipped with a reflected wave reader and a terminal equipped with a reflector (for example, the present invention). (See Japanese Patent Application No. 2005-318436 already assigned to the applicant). In this system, the host and the terminal each have a function to transmit data length information indicating the data length to be transmitted and a frame including a data string having a length corresponding to the data length information to each other, and further, reflected wave transmission Even when an error occurs on the road and the transmission / reception timing between the host and the terminal is lost, a function for quickly recovering the transmission / reception timing is provided, and bidirectional data communication can be suitably realized.

  However, in the reflected wave transmission system, the reflector cannot make a data transmission request by itself, and there is a problem that data transmission cannot be started unless an unmodulated carrier is sent from the reflected wave reader.

  For this reason, the reflected wave reader must always send an unmodulated carrier and wait for reception from the reflector, which wastes power. In order to make the reflected wave reader recognize the existence of its own station and to secure the connection state between the two, the reflector is periodically connected to the unmodulated carrier even when there is no transmission data. In other words, it is necessary to return some reflected wave signal, which wastes power.

  In particular, considering that a terminal equipped with a reflected wave is a battery-powered device such as a digital video camera, a digital still camera, or a mobile phone, the power consumption associated with the communication operation in the absence of transmission data is heavy.

Japanese Patent Laid-Open No. 01-182784 JP 2005-64822 A

  An object of the present invention is to provide a reflected wave that can suitably perform data transmission by returning a modulated reflected wave in which transmission data is superimposed on an unmodulated carrier wave transmitted from the reflected wave reader side. It is an object of the present invention to provide a wireless communication system and a wireless communication apparatus having an excellent transmission method.

  A further object of the present invention is to provide an excellent radio communication system and radio communication apparatus capable of reducing power consumption by suppressing useless transmission / reception operations in a reflector and a reflected wave reader in the absence of transmission data. Is to provide.

The present invention has been made in consideration of the above-described problems, and includes a terminal equipped with a reflector that superimposes transmission data on a reflected wave with respect to an unmodulated carrier, an unmodulated carrier, and data from the modulated reflected wave signal. A wireless communication system comprising a host equipped with a reflected wave reader for reading,
Two-way communication is performed between the terminal and the host for exchanging frames including header information describing the data length.
The host transmits a non-modulated carrier in the transmission section on the terminal side and receives a modulated reflected wave signal from the terminal, transmits a modulated signal carrying a data frame in the transmission section on the host side,
The terminal and the host transmit a null frame consisting only of header information in which 0 is written as the data length when there is no transmission data in their transmission section, and immediately when their control frame is received in the reception section Switch to
This is a wireless communication system.

  However, “system” here refers to a logical collection of a plurality of devices (or functional modules that realize specific functions), and each device or functional module is in a single housing. It does not matter whether or not (hereinafter the same).

  The present invention relates to a wireless communication system using radio wave reflection technology, which includes a reflector that transmits reflected waves with superimposed data and a reflected wave reader that reads data from the reflected waves from the reflector. . According to this type of communication system, since no carrier generation source is required on the reflector side, data transmission can be performed with extremely low power consumption, with an overwhelming performance difference compared to a general wireless LAN. is there.

  However, in the reflected wave transmission system, the reflector cannot make a data transmission request by itself, and there is a problem that data transmission cannot be started unless an unmodulated carrier is sent from the reflected wave reader. For this reason, the reflected wave reader must always send an unmodulated carrier and wait for reception from the reflector, which wastes power. In addition, in order to make the reflected wave reader recognize the existence of the own station and to ensure the connection state between the two, the reflector is periodically used for an unmodulated carrier even when there is no transmission data. It is necessary to return some reflected wave signal to the power source, wasting power.

  On the other hand, in the wireless communication system according to the present invention, when there is no transmission data in its transmission section, the terminal and the host transmit a control frame consisting only of header information in which 0 is written as the data length, and in the reception section. When the control frame is received, switching to its own transmission is immediately performed.

  For example, if there is no transmission data in its own transmission section, the terminal starts data transmission after waiting for generation of data to be transmitted for a predetermined transmission waiting time. As a result, the terminal can reduce power consumption by reducing the number of useless transmission / reception operations.

  In addition, the terminal transmits a null frame when data to be transmitted does not occur even when waiting for a predetermined transmission waiting time in its own transmission interval. Until the host receives any signal from the terminal, it sends an unmodulated carrier and waits for reception. In response to this null frame, the host stops transmission of the unmodulated carrier and immediately transmits its own transmission. Switching to operation can be performed.

  In the wireless communication system according to the present invention, a control frame for passing transmission / reception stop time information between the terminal and the host can be defined. This control frame may also be a null frame with a data length of 0 consisting only of header information.

  In this case, it is possible to introduce a mechanism for notifying the other party of the next transmission / reception timing through a control frame for notifying the transmission / reception stop time information. That is, the terminal or the host transmits the control frame when there is no transmission data in its transmission section, stops the communication operation for the transmission / reception stop time, and switches to reception when the transmission / reception stop time elapses. To resume. Further, when the control frame is received in its own reception section, the communication operation is stopped based on the transmission / reception stop time information, and when the transmission / reception stop time elapses, the communication operation is resumed by switching to transmission.

  Therefore, when the terminal and the host receive this control frame from the other party and there is no transmission data, the terminal and the host shift to the sleep state based on the transmission / reception stop time information and transmit / receive after the stop time has elapsed. By restarting the operation, it is possible to reduce power consumption by reducing the number of useless transmission / reception operations in a period in which no transmission data exists.

  According to the present invention, there is provided an excellent wireless communication system and wireless communication apparatus capable of reducing power consumption by suppressing useless transmission / reception operations in a reflector and a reflected wave reader in a state where there is no transmission data. Can be provided.

  According to the wireless communication system of the reflected wave transmission system according to the present invention, there is no transmission data on the terminal side equipped with the reflector, and no data frame is received from the host equipped with the reflected wave reader. In this case, the terminal waits for generation of data to be transmitted for a while and then starts data transmission. As a result, when there is no transmission data, it is possible to reduce power consumption by reducing the number of useless transmission / reception operations on the terminal side.

  Further, according to the radio communication system of the reflected wave transmission system according to the present invention, a control frame for passing transmission / reception stop time information between the terminal equipped with the reflector and the host equipped with the reflected wave reader is defined, It is possible to introduce a mechanism for notifying each other of the next transmission / reception timing. Therefore, on the communication station side that has received this control frame, for example, when there is no transmission data in its own station, it shifts to the sleep state based on the transmission / reception stop time information and resumes the transmission / reception operation after the stop time has elapsed. By doing so, it is possible to reduce power consumption by reducing the number of useless transmission / reception operations in both the terminal and the host.

  Other objects, features, and advantages of the present invention will become apparent from more detailed description based on embodiments of the present invention described later and the accompanying drawings.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  The present invention relates to a wireless communication system using radio wave reflection technology, which includes a reflector that transmits reflected waves with superimposed data and a reflected wave reader that reads data from the reflected waves from the reflector. . When data is transmitted from the reflector side, the reflected wave reader transmits an unmodulated carrier wave, and the reflector uses a load impedance operation such as on / off of the end of the antenna, and responds to the transmission data with respect to the unmodulated carrier wave. Data is transmitted by performing the modulation process. On the reflected wave reader side, the reflected data can be received and demodulated / decoded to obtain transmission data. Here, the basic configuration of the wireless communication system will be described first.

  FIG. 1 schematically shows a configuration of a wireless communication system according to an embodiment of the present invention.

  FIG. 1A shows the configuration of the host 1 equipped with a reflected wave reader. The host 1 performs a reflected wave transmission operation such as reception of a modulated reflected wave signal from the terminal 2 with no modulation or transmission of a modulated carrier, and a communication control function for controlling a communication operation in the RF function unit 11 And a host function unit 13 for processing data exchanged between the unit 12 and the terminal 2. The host function unit 13 is, for example, a personal computer that stores, edits, manages, outputs video, or prints out image data acquired from a digital camera serving as the terminal 2.

  The communication control function unit 12 controls the transmission / reception timing of data according to a modulation function unit 122 that performs modulation processing of transmission data, a demodulation function unit 123 that performs demodulation processing of received data from the terminal 2, and a predetermined reflected wave transmission protocol. The protocol control unit 121 is provided.

  FIG. 1B shows the configuration of the terminal 2 equipped with a reflector. The terminal 2 performs an operation for receiving a transmission signal transmitted on a modulated carrier and a reflected wave transmission operation for placing transmission data on a reflected wave for an unmodulated carrier, and a communication operation in the RF function unit 21 The communication control function unit 22 that controls the data and the terminal function unit 23 that processes data exchanged with the host 1. The terminal function unit 23 is, for example, a digital camera that generates transmission data to the host 1.

  The communication control function unit 22 controls the transmission / reception timing of data according to a modulation function unit 222 that performs modulation processing of transmission data, a demodulation function unit 223 that performs demodulation processing of received data from the host 1, and a predetermined reflected wave transmission protocol. The protocol control unit 221 is provided.

  The transmission data supplied from the host function unit 13 is subjected to modulation processing in the modulation function unit 121 in the host communication function unit 22 via the control interface 15. The modulated signal 16 is transmitted to the terminal 2 on the carrier 31 generated by the carrier generation source 111 of the RF function unit 11.

  Further, the RF function unit 21 of the terminal 2 receives the carrier (unmodulated carrier or ASK modulated carrier) 31 and obtains the demodulated signal 27. The demodulated signal 27 is demodulated by the demodulation processing unit 223 in the communication control function unit 22 and is received by the terminal function unit 23 via the control interface 25.

  On the other hand, the transmission data supplied from the terminal function unit 23 of the terminal 2 is modulated (primary modulation) by the modulation function unit 222 of the communication control function unit 22. The modulated signal 26 is transmitted to the host 1 on the reflected wave 32 obtained by detecting the carrier 31 received from the host 1 in the RF function unit 21.

  When receiving the reflected wave signal 32, the RF function unit 11 on the host 1 side obtains the demodulated signal 17. The demodulated signal 16 is demodulated by the demodulation function unit 123 in the communication control function unit 12 and supplied to the host function unit 13 through the control interface 15.

  In the reflected wave transmission, for example, a 2.4 GHz band called ISM (Industry Science Medical band) is used as the frequency of the radio wave. Here, the mechanism of the reflected wave transmission operation realized between the RF function unit 21 on the terminal 2 side and the RF function unit 11 on the host 1 side will be described.

  The RF function unit 21 on the terminal 2 side includes an antenna 24, an antenna switch 211, an antenna load 212, a bandpass filter 213, and an ASK detection unit 214, and operates as a reflector.

  When the antenna switch 211 is on, the antenna 23 is terminated with, for example, a 50Ω antenna load 212. When the antenna switch 211 is off, the antenna 24 is open. With such a switching operation, the unmodulated carrier 31 coming from the host 1 can be terminated when it is turned on, and reflected when it is turned off, and the reflected wave can be modulated. The modulation function unit 222 performs an on / off operation of the antenna switch 211 according to the bit image of the transmission data from the terminal function unit 21. For example, when the data is 1, the antenna switch 102 is turned on, and when the data is 0, the antenna switch 102 is turned off, and the data is transmitted as the modulated reflected wave signal 32 with respect to the unmodulated carrier due to the fluctuation of the antenna load impedance.

  The bandpass filter (BPF) 213 and the ASK detection unit 214 are used, for example, when receiving an ASK modulation signal (delivery confirmation signal or data) 31 from the host 1 side. The control is performed by the demodulation function unit 223. However, when one-way communication is performed from the terminal 2 side, these three blocks are unnecessary.

  The RF function unit 11 on the host 1 side includes a 2.4 GHz band antenna 14, an antenna switch that selectively connects the antenna 14 according to transmission / reception operations, or a circulator 117 that replaces the antenna switch, a low noise amplifier 114, A reception system including a quadrature detection unit 115 and an AGC amplifier 116, a transmission system including a frequency synthesis unit 112 for up-converting a transmission signal and a power amplifier 113, and a frequency synthesizer 111 are provided.

  By applying a DC voltage from the modulation function unit 122 to the frequency synthesis unit 112, the unmodulated carrier 31 can be transmitted. The frequency of the unmodulated carrier is determined by the frequency of the frequency synthesizer 111. In the present embodiment, a 2.4 GHz band called ISM is used (same as above). The unmodulated carrier output from the frequency synthesizer 112 is amplified to a predetermined level by the power amplifier 112 and is transmitted from the antenna 14 via the circulator 117.

  On the other hand, the modulated reflected wave signal 32 from the RF function unit 21 on the terminal 2 side as a reflector has the same frequency as that of the unmodulated carrier 31 described above. The modulated reflected wave signal 32 is received by the antenna 14 and input to the above-described reception system via the circulator 117. Since the same local frequency as that at the time of transmission is input to the quadrature detection unit 115, the modulated wave multiplied on the terminal 2 side appears at the output of the quadrature detection unit 115. However, since the received signal has a phase different from that of the local signal, a modulation signal corresponding to the phase difference appears in the I-axis signal and the Q-axis signal.

  In the AGC amplifier unit 116, the gain is controlled to the optimum value, and the output signal is passed to the demodulation function unit 123. The demodulation function unit 123 demodulates the digital data from the I-axis and Q-axis signals, and then decodes the data to correct data. When the data delivery confirmation is performed with respect to the terminal 2, the modulation function unit 122 sends the digital data of the acknowledgment Ack if the received packet data is correct, or the negative Nack digital data if the received packet data is correct. And apply ASK modulation. Whether the data is correct or not is determined by the CRC code added to the image data packet.

  Then, the protocol control unit 121 on the host 1 side and the protocol control unit 221 on the terminal 2 side realize protocol control such as connection and disconnection of such a reflected wave transmission line and transmission / reception timing. In this embodiment, transmission / reception timing control is performed in consideration of low power consumption when there is no transmission data. Details of this point will be described later.

  In the data transmission based on the reflected wave transmission, the RF function unit 21 on the terminal 2 side does not require a carrier generation source, so that the data transmission operation can be driven with low consumption. The antenna switch 211 for changing the load impedance of the antenna in the RF function unit 21 is generally composed of a gallium arsenide IC and its power consumption is several tens of μW or less. Therefore, in the unidirectional transmission using the modulated reflected wave signal, Data transmission is possible at several tens of μW. This is an overwhelming performance difference compared to the average power consumption of a general wireless LAN.

  Further, in the uplink from the RF function unit 21 on the terminal 2 side, high-speed communication can be realized by adopting a multi-level modulation method such as BPSK or QPSK (see, for example, WO 2005/36767) thing). On the other hand, in the downlink from the RF function unit 11 of the host 1, ASK modulation is used in consideration of the ease of detection of the RF function unit 21 on the terminal 2 side. Low data rate.

  Subsequently, a communication operation in the wireless communication system according to the present embodiment will be described.

  The above-described wireless communication system is basically configured by one-to-one data communication between the terminal 2 and the host 1. In this case, the transmission ratio in each direction is not always constant. For example, when a reflector is mounted on a mobile phone as the terminal 2 and a reflected wave reader is attached to the charging stand for two-way communication, when uploading an image taken with a digital camera in the mobile phone, When downloading music data from a charging stand to a mobile phone, the required bandwidth varies greatly.

  Therefore, in this embodiment, a method of transmitting a variable-length transmission frame according to the transmission data amount is adopted. In this case, the data transmission source configures a transmission frame including a data string having a length corresponding to the data length information including a data length information bit indicating a data length to be transmitted. FIG. 2 shows a configuration example of a variable-length transmission frame used in the wireless communication system according to the present embodiment.

  One transmission frame includes a preamble 310 for synchronizing modulation, a frame synchronization bit (unique word) 320 for frame synchronization, header information 330, header error detection bits and error correction bits 340. And data (payload) 350, data error detection bits and error correction bits 360.

  The frame type 331 of the header information 330 represents whether the transmission frame is a control frame or a data frame. The frame parameter 332 represents further detailed information on the frames classified by the frame type 331. For example, when the frame type 331 indicates that the transmission frame is a control frame, a connection control frame, a disconnection control frame, or a control frame for instructing a transmission / reception operation stop (described later) by the frame parameter 332. ). The frame sequence number 333 represents a number added to the frame in order to perform sequence control. The Ack / Nack information 434 is an information bit for notifying the other party whether or not the data portion of the previously received frame has been normally received. Further, the host 1 and the terminal 2 represent the length of the data (payload) with the data length 335 included in the header information, and notify the communication partner.

  According to the sequence of exchanging variable length frames, when the amount of downlink transmission data from the host 1 is large and the amount of uplink transmission data from the terminal 2 is small, the downlink throughput is improved. When the amount of uplink transmission data is large and the amount of downlink transmission data is small, uplink throughput is improved.

  FIG. 3 shows an example of a frame exchange sequence in the wireless communication system when the variable length frame shown in FIG. 2 is used.

  The terminal 2 transmits a data frame 400 to the host 1 on a reflected wave with respect to the unmodulated carrier wave 405 from the host 1. On the other hand, when the host 1 receives the data frame 400, the host 1 calculates the data reception time 402 from the data length included in the header information, and performs the reception operation of the reflected wave signal only during that period.

  After completing the transmission of the data frame 400, the terminal 2 starts a reception operation after a predetermined guard time 401 has elapsed. In addition, when the data reception time 402 expires, the host 1 starts transmission of the data frame 403 from itself after a predetermined guard time 401 has elapsed.

  Thereafter, when transmission of the data frame 403 is completed, the host 1 starts transmission of the non-modulated carrier 405 again after a predetermined guard time 404 has elapsed, and performs an operation of receiving a reflected wave signal from the terminal 2.

  On the other hand, the terminal 2 calculates the data reception time 406 from the data length included in the header information of the data frame 403 received from the host 1. Then, when the data reception time 406 expires, the terminal 2 waits for a predetermined guard time 404 and then shifts to a transmission operation (that is, a modulation operation for a reflected wave).

  By repeating the above, the host 1 and the terminal 2 send data frames alternately to perform data transmission / reception in both directions.

  Here, in a wireless communication system using reflected wave transmission, the reflector cannot make a data transmission request by itself, and cannot transmit data unless an unmodulated carrier is sent from the reflected wave reader. There is.

  By continuously sending an unmodulated carrier from the host 1, the terminal can make a data transmission request at any time. However, the host must wait for reception, and the power can be transmitted even when there is no transmission data. Waste.

  In addition, the terminal 2 makes the host 1 recognize the existence of its own station, and in order to ensure the connection state between the two, even if there is no transmission data, the terminal 2 periodically It is necessary to return a reflected wave signal (for example, a null signal in which only 0 is described), and power is wasted for operations other than data transmission.

  For example, in the case of a system that performs a variable-length frame exchange sequence as shown in FIG. 3, each of the host 1 and terminal 2 sets the data length of the header information to 0 when there is no transmission data, and data and data error detection bits. It is also possible to form a data frame that does not include (hereinafter also referred to as “null frame”) and notify the communication partner that there is no transmission data. FIG. 4 shows an example of a frame exchange sequence when notifying each other that there is no transmission data using a null frame.

  The terminal 2 transmits a data frame 500 to the host 1 on a reflected wave with respect to the unmodulated carrier wave 505 from the host 1. Then, after completing the transmission of the data frame 500, the terminal 2 starts a reception operation after a predetermined guard time 501 has elapsed.

  When the host 1 receives the data frame 500, the host 1 calculates a data reception time 502 from the data length included in the header information. Then, when the data reception time 502 expires, the host 1 starts transmission of the data frame 503 by itself after a predetermined guard time 501 elapses. Thereafter, after a predetermined guard time 504 elapses, the host 1 starts transmission of the unmodulated carrier 505 again and receives a reflected wave signal from the terminal 2.

  On the other hand, the terminal 2 calculates the data reception time 506 from the data length included in the header information of the data frame 503 received from the host 1, and transmits after the data reception time 506 has expired and further waits for the guard time 504. Recognize that the action can begin. Here, if there is no transmission data, the terminal 2 sets the data length of the header information to 0 and transmits a null frame 510 that does not include data and data error detection bits.

  When receiving the null frame 510, the host 1 recognizes that the transmission operation can be started by itself after a predetermined guard time 501 elapses after the reception of the header information. Here, the host 1 similarly transmits a null frame 530 when there is no transmission data.

  When receiving the null frame 530 from the host 1, the terminal 2 recognizes that the transmission operation can be started after waiting for a predetermined guard time 504 when reception of the header information is completed. Here, when there is no transmission data, the terminal 2 sets the data length of the header information to 0 and transmits a null frame not including data and data error detection bits.

  The host 1 starts sending the unmodulated carrier 505 after a predetermined guard time 504 has elapsed since the transmission of the null frame 530. Here, when receiving the null frame from the terminal 2, when the reception of the header information is completed, it is recognized that the transmission operation can be started by itself after a predetermined guard time 501 has elapsed.

  In this way, until transmission data is generated by either the host 1 or the terminal 2, a sequence of exchanging null frames after each guard time 501 or 504 is repeated.

  According to the frame exchange sequence as described above, the host 1 and the terminal 2 are referred to as a null frame even when there is no transmission data in order to maintain the connection state of the transmission path and adjust the transmission / reception timing of each other. A wasteful communication operation of repeatedly transmitting a signal that does not contain data must be performed. In particular, considering that the terminal is a battery-powered device such as a digital video camera, a digital still camera, or a mobile phone, the power consumption associated with signal transmission only for maintaining the connection state is heavy.

  Therefore, in the wireless communication system according to the present embodiment, when there is no transmission data on the terminal 2 side and no data frame is received from the host 1, the terminal 2 transmits data to be transmitted for a while. Data transmission is started after waiting for the occurrence. As a result, when there is no transmission data, the terminal 2 can reduce power consumption by reducing the number of useless transmission / reception operations.

  FIG. 5 to FIG. 8 show, in the form of flowcharts, the operation procedures of the reception operation, the operation switching from reception to transmission, the transmission operation, and the operation switching from transmission to reception executed by the terminal 2 in this case. Hereinafter, the operation procedure of the terminal 2 will be described with reference to each flowchart.

  When the terminal 2 starts reception, the terminal 2 first detects a frame synchronization bit (step S1). The terminal 2 repeatedly evaluates the received data string until it detects a frame synchronization bit or times out the detection time (No in step S1).

  When the detection time has timed out, the terminal 2 determines the Ack / Nack information to be transmitted in the next frame as Nack (step S5), and completes reception. Thereafter, the terminal 2 performs a transmission / reception switching operation.

  Further, when the frame synchronization bit is detected (Yes in Step S1), the terminal 2 determines whether or not there is an error in the header after obtaining the header information (Step S2). If there is an error in the header (Yes in step S2), the Ack / Nack information is fixed to Nack (step S5), and the reception is completed. Thereafter, the terminal 2 performs a transmission / reception switching operation.

  On the other hand, if there is no error in the header (No in step S2), the terminal 2 calculates a data reception time from the data length information, and performs a data reception operation over the data reception time (step S3). Then, when the data reception is completed, the terminal 2 determines whether or not there is an error in the data, determines Ack / Nack information to be placed in the header of the next transmission frame (step S4), and completes the reception. Thereafter, the terminal 2 performs a transmission / reception switching operation.

  After completing the reception operation for the data reception time corresponding to the data length described in the header part of the transmission frame from the communication partner, the terminal 2 sets a predetermined guard time (step S11), and then performs the transmission operation. Migrate to

  Then, the terminal 2 checks whether it is necessary to return Ack or Nack information to the host 1 at the start of transmission (step S21). In the reception processing operation shown in FIG. 5, when valid reception data exists (data length ≠ 0) and data error detection is performed, it is determined that Ack or Nack information needs to be returned, and is determined from the detection result. A data frame including the received Ack or Nack information is formed (step S22), and is transmitted from the RF function unit 21.

  Further, when there is no valid received data (data length = 0), when frame synchronization bit detection times out, or when a header error is detected, it is determined that there is no need to return Ack or Nack information. Then, the terminal 2 checks whether or not there is transmission data of itself (step S23).

  Here, when there is transmission data, the terminal 2 forms a transmission frame for transmitting the transmission data, and transmits this to the host 1 from the RF function unit 21 (step S22).

  On the other hand, when there is no transmission data, the terminal 2 waits whether data to be transmitted is generated for a predetermined period. When transmission data is generated, a transmission frame is constructed and transmitted in the same manner as described above (step S22). However, if no transmission data is generated even after a predetermined period of time has elapsed, the data length of the header information is set to 0, a null frame not including data and data error detection bits is formed, and this is transmitted from the RF function unit 21 ( Step S22).

  The terminal 2 provides a predetermined guard time after completing the transmission of the transmission frame until starting the reception operation (step S31). When the guard time elapses, the reception operation is started again, and thereafter the same operation is repeated.

  Note that the value of the transmission data standby time in the terminal 2 is a fixed value, and is set by the host function unit 23 or dynamically, such as extending the standby time every time a null frame exchange is repeated. A function to change can also be added.

  FIG. 9 shows the communication operation of the terminal 2 shown in FIGS. 5 to 8 in the form of a state transition diagram.

  When the reception data is completed and the transmission data exists (here, the Ack / Nack information is also included in the transmission data), the terminal 2 shifts to the transmission state after a predetermined guard time. Start transmission operation.

  If the transmission data does not yet exist when the reception state is completed, the terminal 2 shifts to a standby state for a predetermined period after a predetermined guard time.

  When transmission data is generated in the standby state, the terminal 2 starts a transmission operation. When the standby state times out, a null frame transmission operation is started.

  And the terminal 2 will return to a receiving state, if transmission of a data frame or a null frame is completed.

  10 to 13 show the reception operation executed by the host 1 which is the communication partner of the terminal 2 performing the communication operation as described above, the operation switching from reception to transmission, the transmission operation, and the operation switching from transmission to reception. Each operation procedure is shown in the form of a flowchart. Hereinafter, the operation procedure of the host 1 will be described with reference to each flowchart.

  When the host 1 starts reception (step S41), it first detects a frame synchronization bit. Then, the host 1 repeatedly evaluates the received data string until it detects a frame synchronization bit or times out the detection time (No in step S41).

  When the detection time has timed out, the host 1 determines the Ack / Nack information to be transmitted in the next frame as Nack (step S45), and completes reception.

  Further, when the frame synchronization bit is detected (Yes in step S41), the host 1 determines whether or not there is an error in the header after obtaining the header information. If there is an error in the header (Yes in step S42), the Ack / Nack information is determined as Nack and the reception is completed.

  On the other hand, if there is no error in the header (No in step S42), the host 1 calculates the data reception time from the data length information, and performs the data reception operation over the data reception time (step S43). When the host 1 completes the data reception, it determines whether or not there is an error in the data, determines the Ack / Nack information to be placed in the header of the next transmission frame (step S44), and completes the reception.

  If it is determined from the data length information of the header that the data length is 0, there is no valid data acquired by data reception in step S43, and therefore the host 1 does not detect data errors and does not detect Ack / Nack. The information is confirmed as Nack (step S44), and the reception flow is terminated.

  The host 1 provides a predetermined guard time after completing the reception operation for the data reception time corresponding to the data length described in the header portion of the transmission frame from the communication partner until starting transmission ( Step S51). When the guard time elapses, a transmission operation is started, a frame for transmitting own transmission data is formed (step S52), and the transmission is completed to the RF function unit 11.

  The host 1 provides a predetermined guard time after completing the transmission of the transmission frame until starting the reception operation (step S53). When the guard time elapses, the reception operation is started again, and thereafter the same operation is repeated.

  FIG. 14 shows the communication operation of the host 1 shown in FIGS. 10 to 13 in the form of a state transition diagram.

  When the reception state is completed, the host 1 starts the transmission operation after measuring the transmission / reception switching guard time. When the transmission state is completed, this time, after measuring the transmission / reception switching guard time, the state shifts to the reception state.

  FIG. 15 shows an example of a frame exchange sequence in the wireless communication system in a case where the terminal 2 in a transmission state operates so as to start data transmission after waiting for generation of data to be transmitted for a while.

  The terminal 2 transmits a data frame 600 to the host 1 on the reflected wave with respect to the unmodulated carrier wave 605 from the host 1. On the other hand, when the host 1 receives the data frame 600, the host 1 calculates the data reception time 602 from the data length included in the header information, and performs the reception operation of the reflected wave signal only during that period.

  After completing the transmission of the data frame 600, the terminal 2 starts a reception operation after a predetermined guard time 601 has elapsed. Further, when the data reception time 602 expires, the host 1 starts transmission of a data frame 603 from itself after a predetermined guard time 601 elapses. The terminal 2 calculates the data reception time 606 from the data length included in the header information of the data frame 603, and performs the reception operation only during that period.

  Thereafter, when transmission of the data frame 603 is completed, the host 1 starts transmission of the unmodulated carrier 605 again after a predetermined guard time 604 has elapsed, and performs an operation of receiving a reflected wave signal from the terminal 2.

  When the data reception time 606 expires, the terminal 2 further waits for a predetermined guard time 604 and then transmits the Ack frame 610 for the data frame 603 by reflected wave transmission. Here, it is assumed that the transmission / reception operation of the data frame 603 is performed successfully, and the Ack frame 610 is composed of only header information, and 0 is written in the data length of the header information.

  When the host 1 receives the Ack frame 610, from the data length included in the header information, when the reception of the header is completed, the host 1 immediately starts measuring the guard time 601 and then becomes ready for transmission. Here, since there is no transmission data, the host 1 sets the data length of the header information to 0 and transmits a null frame 630 that does not include data and data error detection bits. Then, after a predetermined guard time 604 elapses, the host 1 starts sending the unmodulated carrier 605 again and performs an operation of receiving a reflected wave signal from the terminal 2.

  When the terminal 2 receives the null frame 630 from the host 1, it recognizes that the transmission operation can be started after waiting for the guard time 604. Here, when there is no transmission data, the terminal 2 waits for generation of data to be transmitted for a predetermined period 607. When transmission data is generated in this period 607, a reflected wave transmission operation of the data frame is performed. If no transmission data is generated, a null frame 620 is transmitted as shown in the figure.

  When the host 1 receives the null frame 620 from the terminal 2, the host 1 recognizes that the transmission operation can be started by itself after a predetermined guard time 601 elapses.

  In this way, until transmission data is generated by either the host 1 or the terminal 2, the host 1 transmits the null frame 630 after the guard time 601 elapses, and the terminal 2 is in its own transmission station. After waiting for transmission data for a predetermined period 607, the sequence of transmitting the null frame 620 is repeated.

  According to the frame exchange sequence as shown in FIG. 15, the terminal 2 starts data transmission after waiting for generation of data to be transmitted for a while (transmission data waiting time 607 in FIG. 15). When there is no transmission data, the terminal 2 can reduce power consumption by reducing the number of useless transmission / reception operations compared to the sequence shown in FIG.

  In addition, as another method for suppressing unauthorized transmission / reception when there is no transmission data, a control frame for passing transmission / reception stop time information between terminal 2 and host 1 is defined, and the next transmission / reception timing is notified to each other. It is conceivable to introduce a mechanism to play with each other. In this case, the communication station that has received the control frame stops the transmission / reception operation based on the transmission / reception stop time information, and restarts the transmission / reception operation after the stop time has elapsed. As a result, when there is no transmission data, the number of useless transmission / reception operations in both the terminal 2 and the host 1 can be reduced, and power consumption can be reduced.

  Similar to the above-described null frame, the control frame can be configured as a data frame in which the data length of the header information is 0 and does not include data and data error detection bits. Can be represented by the value of.

  FIG. 16 to FIG. 20 show the operation procedure of the reception operation, the operation switching from reception to transmission, the transmission operation, the operation switching from transmission to reception, and the sleep performed by the terminal 2 when notifying each other of the transmission / reception time information. It is shown in the form of a flowchart. Hereinafter, the operation procedure of the terminal 2 will be described with reference to each flowchart.

  When the terminal 2 starts reception, the terminal 2 first detects a frame synchronization bit (step S61). The terminal 2 repeatedly evaluates the received data string until it detects a frame synchronization bit or times out the detection time (No in step S61).

  If the detection time has timed out, the terminal 2 determines the Ack / Nack information to be transmitted in the next frame as Nack (step S67) and completes reception. Thereafter, the terminal 2 performs a transmission / reception switching operation.

  Further, when the frame synchronization bit is detected (Yes in Step S61), the terminal 2 determines whether or not there is an error in the header after obtaining the header information (Step S62). If there is an error in the header (Yes in step S62), the Ack / Nack information is determined as Nack (step S67), and the reception is completed. Thereafter, the terminal 2 performs a transmission / reception switching operation.

  On the other hand, if there is no error in the header (No in step S62), the terminal 2 subsequently checks whether or not the received frame is a null frame (step S63). Here, when the received frame is a null frame, the transmission / reception waiting time information described in the header information is read to set the transmission / reception waiting time (step S64), and the reception operation is completed. Thereafter, the terminal 2 shifts to the sleep state for the transmission / reception waiting time.

  When the frame received from the host 1 is a normal data frame (No in step S63), the terminal 2 reads the data length information from the header information and calculates the data reception time, and the data is received over the data reception time. Is received (step S65). Then, when the data reception is completed, the terminal 2 determines whether or not there is an error in the data, determines the Ack / Nack information to be placed in the header of the next transmission frame (step S66), and completes the reception. Thereafter, the terminal 2 performs a transmission / reception switching operation.

  The terminal 2 completes the reception operation for the data reception time corresponding to the data length described in the header part of the transmission frame from the communication partner, and then provides a predetermined guard time (step S71), and then performs the transmission operation. Migrate to

  Then, at the start of transmission, the terminal 2 checks whether it is necessary to return Ack or Nack information to the host 1 (step S81). In the reception processing operation shown in FIG. 16, when valid received data exists (data length ≠ 0) and data error detection is performed, it is determined that it is necessary to return Ack or Nack information, and is determined from the detection result. A data frame including the received Ack or Nack information is formed (step S82), and is transmitted from the RF function unit 21. Thereafter, the terminal 2 performs a transmission / reception switching operation.

  Further, when there is no valid received data (data length = 0), when frame synchronization bit detection times out, or when a header error is detected, it is determined that there is no need to return Ack or Nack information. Subsequently, the terminal 2 checks whether or not its own transmission data exists (step S83).

  Here, when there is transmission data, the terminal 2 forms a transmission frame for transmitting the transmission data, and transmits this to the host 1 from the RF function unit 21 (step S82). Thereafter, the terminal 2 performs a transmission / reception switching operation.

  On the other hand, when there is no transmission data, the terminal 2 forms a null frame including the value of the transmission / reception waiting time (step S84), and transmits this to the host 1 from the RF function unit 21 (step S82). Thereafter, the terminal 2 shifts to the sleep state for the transmission / reception waiting time.

  The terminal 2 provides a predetermined guard time after completing the transmission of the transmission frame until starting the reception operation (step S91). When the guard time elapses, the reception operation is started again, and thereafter the same operation is repeated.

  When the terminal 2 transmits a null frame in the transmission operation procedure, the terminal 2 sets the sleep state for the transmission / reception waiting time described in the null frame (step 101), and then executes the transmission / reception switching operation, and then receives it. Start operation. Further, when the terminal 2 receives a null frame from the host 1 in the reception operation procedure, the terminal 2 sets the sleep state for the transmission / reception waiting time described in the null frame (step 101), and then performs the transmission / reception switching operation. After execution, the transmission operation is started.

  21 to 25 show the reception operation executed by the host 1 when notifying each other of transmission / reception time information, the operation switching from reception to transmission, the transmission operation, the operation switching from transmission to reception, and the operation procedure of sleep, respectively. It is shown in the form of a flowchart. Hereinafter, the operation procedure of the host 1 will be described with reference to each flowchart.

  When the host 1 starts reception, the host 1 tries to detect a frame synchronization bit by transmitting an unmodulated carrier (step S111).

  Here, when the frame synchronization bit is detected (Yes in Step S111), the host 1 determines whether or not there is an error in the header after obtaining the header information (Step S112). If there is an error in the header information, the process returns to step S111 and the detection of the frame synchronization bit is repeated.

  On the other hand, if there is no error in the header (No in step S112), the host 1 subsequently checks whether the received frame is a control frame instructing waiting for transmission / reception (step S113).

  When the frame received from the terminal 2 is a control frame, the host 2 reads the transmission / reception waiting time information described in the header information and sets the sleep time based on the transmission / reception waiting time information in the header information (step S114), the receiving operation is completed. Thereafter, the host 1 shifts to the sleep state for the transmission / reception waiting time.

  When the frame received from the terminal 2 is a normal data frame (No in step S112), the host 1 reads the data length information from the header information to calculate the data reception time, and the data is received over the data reception time. Is received (step S115). When the host 1 completes the data reception, it determines whether or not there is an error in the data, determines the Ack / Nack information to be placed in the header of the next transmission frame (step S116), and completes the reception. Thereafter, the host 1 performs a transmission / reception switching operation.

  The host 1 completes the reception operation for the data reception time corresponding to the data length described in the header part of the transmission frame from the communication partner, and then provides a predetermined guard time (step S121), and then performs the transmission operation. Migrate to

  Then, the host 1 checks whether it is necessary to return Ack or Nack information to the terminal 2 when starting transmission (step S131). In the reception processing operation shown in FIG. 21, when valid reception data exists (data length ≠ 0) and data error detection is performed, it is determined that it is necessary to return Ack or Nack information. A data frame including the confirmed Ack or Nack information is formed (step S132), and this is transmitted from the RF function unit 11. Thereafter, the host 1 performs a transmission / reception switching operation.

  Further, when there is no valid received data (data length = 0), when frame synchronization bit detection times out, or when a header error is detected, it is determined that there is no need to return Ack or Nack information. Subsequently, the host 1 checks whether there is transmission data of itself (step S133).

  Here, when there is transmission data, the host 1 configures a transmission frame for transmitting the transmission data, and transmits this to the terminal 2 from the RF function unit 11 (step S132). Thereafter, the host 1 performs a transmission / reception switching operation.

  On the other hand, when there is no transmission data, the host 1 forms a null frame including the value of the transmission / reception waiting time (step S134), and transmits this to the terminal 2 from the RF function unit 11 (step S132). Thereafter, the host 1 shifts to the sleep state for the transmission / reception waiting time.

  The host 1 provides a predetermined guard time after completing the transmission of the transmission frame until starting the reception operation (step S141). When the guard time elapses, the reception operation is started again, and thereafter the same operation is repeated.

  When the host 1 transmits a null frame in the transmission operation procedure, the host 1 sets the sleep state for the transmission / reception waiting time described in the null frame (step 151), and then executes the transmission / reception switching operation, and then receives it. Start operation. Further, when the host 1 receives a null frame from the terminal 2 in the reception operation procedure, the host 1 sets the sleep state for the transmission / reception waiting time described in the null frame (step 151), and then performs the transmission / reception switching operation. After execution, the transmission operation is started.

  FIG. 26 shows the communication operation of the host 1 and the terminal 2 when notifying the transmission / reception time information in the form of a state transition diagram.

  When the host 1 and the terminal 2 complete the reception of a frame other than the control frame for waiting for transmission / reception (or the null frame in which the transmission / reception waiting time is set), the host 1 and the terminal 2 shift to the transmission state after a predetermined guard time and transmit Start operation.

  Further, the host 1 and the terminal 2 shift to a reception state after a predetermined guard time when transmission of a frame other than a control frame for waiting for transmission / reception (or a null frame in which a transmission / reception waiting time is set) is completed. The reception operation is started.

  On the other hand, when the host 1 and the terminal 2 receive a control frame for waiting for transmission / reception (or a null frame in which a transmission / reception waiting time is set), the host 1 and the terminal 2 transition to a sleep state. Then, after waiting for the transmission / reception waiting time described in the control frame (or null frame), the process proceeds to the transmission operation.

  Further, when the host 1 and the terminal 2 transmit a control frame for waiting for transmission / reception (or a null frame in which a transmission / reception waiting time is set), the host 1 and the terminal 2 shift to a sleep state. Then, after waiting for the transmission / reception waiting time described in the control frame (or null frame), the operation shifts to the receiving operation.

  FIG. 27 shows an example of a frame exchange sequence in the wireless communication system when the host 1 and the terminal 2 notify the transmission / reception time information.

  The terminal 2 transmits a data frame 700 to the host 1 on a reflected wave with respect to the unmodulated carrier wave 705 from the host 1. On the other hand, when the host 1 receives the data frame 700, the host 1 calculates the data reception time 702 from the data length included in the header information, and performs the reception operation of the reflected wave signal only during that period.

  After completing the transmission of the data frame 700, the terminal 2 starts a reception operation after a predetermined guard time 701 has elapsed. In addition, when the data reception time 702 expires, the host 1 starts transmission of the data frame 703 from this time after a predetermined guard time 701 has elapsed. The terminal 2 calculates the data reception time 706 from the data length included in the header information of the data frame 703, and performs the reception operation only during that period.

  Thereafter, when the transmission of the data frame 703 is completed, the host 1 starts transmission of the unmodulated carrier 705 again after a predetermined guard time 704 has elapsed, and performs the operation of receiving the reflected wave signal from the terminal 2 .

  When the data reception time 706 expires, the terminal 2 further waits for a predetermined guard time 704 and then transmits the Ack frame 710 for the data frame 703 by reflected wave transmission. Here, it is assumed that the transmission / reception operation of the data frame 703 is performed successfully, and the Ack frame 710 is composed of only header information, and 0 is written in the data length of the header information.

  When the host 1 receives the Ack frame 710, from the data length included in the header information, when the reception of the header is completed, the host 1 immediately starts measuring the guard time 701 and then becomes ready for transmission. Here, since there is no transmission data, the host 1 sets a transmission / reception waiting time, sets the data length of the header information to 0, and transmits a control frame 730 that does not include data and data error detection bits. Further, when the terminal 2 receives the control frame 730 from the host 1, the terminal 2 sets the sleep state 707 for the transmission / reception waiting time described in the header information.

  Then, the host 1 sets the sleep state for the set transmission / reception waiting time, and after the predetermined guard time 604 has elapsed, starts sending the unmodulated carrier 705 again and receives the reflected wave signal from the terminal 2 To do.

  On the other hand, the terminal 2 can release the sleep state after the transmission / reception waiting time elapses, and can start the transmission operation after waiting for the guard time 704. Here, since there is no transmission data, the terminal 2 sets a transmission / reception waiting time, sets the data length of the header information to 0, and transmits a control frame 720 that does not include data and data error detection bits. When the host 1 receives the control frame 720 from the terminal 2, the host 1 sets the sleep state for the transmission / reception wait time described in the header information.

  Thus, the host 1 or the terminal 2 performs a sequence of transmitting the control frame 730 or 720 for notifying the transmission / reception waiting time until the transmission data is generated and repeating the sleep state.

  According to the frame exchange sequence as shown in FIG. 27, when there is no transmission data, the host 1 and the terminal 2 reduce the number of useless transmission / reception operations compared to the sequence shown in FIG. Therefore, low power consumption can be achieved.

  The present invention has been described in detail above with reference to specific embodiments. However, it is obvious that those skilled in the art can make modifications and substitutions of the embodiment without departing from the gist of the present invention.

  In this specification, the present invention is applied to a wireless communication system that adopts a reflected wave transmission method in which a reflector returns a modulated reflected wave in which transmission data is superimposed on an unmodulated carrier wave transmitted from the reflected wave reader side. However, the gist of the present invention is not limited to this. By applying the present invention to a wireless LAN or Bluetooth communication typified by IEEE 802.11, or other wireless communication systems, the terminal and the host can similarly avoid useless transmission / reception operations in the state where there is no transmission data, Electric power consumption can be reduced.

  In short, the present invention has been disclosed in the form of exemplification, and the description of the present specification should not be interpreted in a limited manner. In order to determine the gist of the present invention, the claims should be taken into consideration.

FIG. 1A is a diagram showing a configuration of a host 1 equipped with a reflected wave reader. FIG. 1B is a diagram showing a configuration of the terminal 2 equipped with a reflector. FIG. 2 is a diagram illustrating a configuration example of a variable-length transmission frame. FIG. 3 is a diagram showing an example of a frame exchange sequence when the variable length frame shown in FIG. 2 is used. FIG. 4 is a diagram showing an example of a frame exchange sequence in the case where the null frames are used to notify each other that there is no transmission data. FIG. 5 is a flowchart showing the reception operation of the terminal. FIG. 6 is a flowchart illustrating a procedure for the terminal to switch operation from reception to transmission. FIG. 7 is a flowchart showing the transmission operation of the terminal. FIG. 8 is a flowchart showing a procedure for the terminal to switch the operation from transmission to reception. FIG. 9 is a diagram showing the communication operation of the terminal shown in FIGS. 5 to 8 in the form of a state transition diagram. FIG. 10 is a flowchart showing the reception operation of the host. FIG. 11 is a flowchart showing a procedure for the host to switch the operation from reception to transmission. FIG. 12 is a flowchart showing a host transmission operation. FIG. 13 is a flowchart showing a procedure for the host to switch the operation from transmission to reception. FIG. 14 is a diagram showing the communication operation of the host shown in FIGS. 10 to 13 in the form of a state transition diagram. FIG. 15 is a diagram showing an example of a frame exchange sequence in a case where a terminal in a transmission state operates to start data transmission after waiting for generation of data to be transmitted for a while. FIG. 16 is a flowchart showing the reception operation of the terminal. FIG. 17 is a flowchart illustrating a procedure for the terminal to switch operation from reception to transmission. FIG. 18 is a flowchart showing the transmission operation of the terminal. FIG. 19 is a flowchart showing a procedure for the terminal to switch the operation from transmission to reception. FIG. 20 is a flowchart showing the sleep operation of the terminal. FIG. 21 is a flowchart showing the reception operation of the host. FIG. 22 is a flowchart showing a procedure for the host to switch the operation from reception to transmission. FIG. 23 is a flowchart showing the transmission operation of the host. FIG. 24 is a flowchart showing a procedure for the host to switch the operation from transmission to reception. FIG. 25 is a flowchart showing the sleep operation of the host. FIG. 26 is a diagram showing a state transition diagram of the communication operation of the host 1 and the terminal 2 when notifying each other of transmission / reception time information. FIG. 27 is a diagram illustrating an example of a frame exchange sequence in the wireless communication system when the host 1 and the terminal 2 notify transmission / reception time information.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Host 11 ... RF function part 12 ... Communication control function part 13 ... Host function part 2 ... Terminal 21 ... RF function part 22 ... Communication control function part 23 ... Host function part

Claims (7)

Wireless communication system comprising a terminal equipped with a reflector for superimposing transmission data on a reflected wave for an unmodulated carrier, and a host equipped with a reflected wave reader for transmitting the unmodulated carrier and reading data from the modulated reflected wave signal Because
Two-way communication is performed between the terminal and the host for exchanging frames including header information describing the data length.
The host transmits a non-modulated carrier in the transmission section on the terminal side and receives a modulated reflected wave signal from the terminal, transmits a modulated signal carrying a frame in the transmission section on the host side,
The terminal and the host transmit a null frame consisting only of header information in which 0 is written as the data length when there is no transmission data in their transmission interval, and transmit their own transmission when receiving the control frame in their reception interval. Switch to action,
A wireless communication system. When there is no transmission data in the transmission section of the terminal, the terminal waits for generation of data to be transmitted for a predetermined transmission waiting time, and then starts data transmission.
The wireless communication system according to claim 1. A terminal transmits a null frame when data to be transmitted does not occur even if it waits for a predetermined transmission waiting time in its transmission interval.
The wireless communication system according to claim 2. A control frame for passing transmission / reception stop time information between the terminal and the host is defined,
The terminal or the host transmits the control frame when there is no transmission data in its own transmission interval and stops the communication operation for the transmission / reception stop time, and when receiving the control frame in its own reception interval, the transmission / reception stop time information Stop communication operation based on
The wireless communication system according to claim 1. A wireless communication device that performs reflected wave transmission,
Perform bidirectional communication to exchange frames with header information describing the data length with the communication partner,
When there is no transmission data in its own transmission section, a null frame consisting only of header information with a data length of 0 is transmitted,
When the control frame is received in its own reception section, switching to its own transmission operation is performed.
A wireless communication apparatus. With a reflector function that superimposes transmission data on the reflected wave for an unmodulated carrier,
When there is no transmission data in its own transmission section, it waits for the generation of data to be transmitted for a predetermined transmission waiting time, and when transmission data is generated within the transmission waiting time, a data frame is transmitted and transmission data is generated. Otherwise, send a null frame,
The wireless communication apparatus according to claim 5. A control frame for sending / receiving stop time information is defined,
When there is no transmission data in its own transmission section, the communication operation is stopped for the transmission / reception stop time after transmitting the control frame,
When the control frame is received in its own reception section, the communication operation is stopped based on the transmission / reception stop time information.
The wireless communication apparatus according to claim 5.

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